WO3 | Tungsten oxide basic knowledge
WO3 has a refractive index near 2.2 at 550 nm and a transmittance range from below 400 nm into the IR region. It is a candidate high-index material for the VIS region.
WO3 evaporates at lower temperatures than other high-index materials for the VIS region, such as TiO2 and Ta2O5. And since only a small amount of heating is required, plastic substrates, which cannot endure high temperature, can be used. Among the several applications of WO3, the production of electrochromic layers is more popular than that of AR coatings.
WO3 layers change color when cations are inserted into the crystal structure. WO3 is often mentioned in the context of "smart windows," which control the amount of solar energy that enters a building, and also in relation to large-area displays. For most of these purposes, the so-called electrochromic effect is used, where the coloration or bleaching of tungsten oxide is caused by an electrochromic reaction.